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CD4021

The CD4021 is a common parallel-in serial-out shift register. You can get them at digi-key or many other electronics retailers. They give you multiple inputs all for the price of only 3 pins on the micro-controller. Check out our introductory tutorial on shift registers to get started. These chips are born to be Daisy-Chained, which is what we do with them in our AlphaZed Keyboard.
Shift Registers help you multiply your inputs and outputs....
4 Daisy chained CD4021 shift registers gives us 32 inputs....
Connect shift registers together to get more output and input pins from your microcontroller....
Keyboard kit using CD4021 shift registers and big through hole buttons....
32 buttons for a fully-functioning hand-held USB keyboard....
A QWERTY keyboard you build yourself....
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